Matt Wronkiewicz's Weblog» Programming Projects

Announcing Virtual Range 1.0 for Mac OS X

Matt — Thu, 06 Aug 2009 06:25:51 +0000

I am pleased to announce version 1.0 of Virtual Range, my rocket simulator for Mac OS X. Virtual Range can simulate the flight of a rocket model in real time (on sufficiently powerful CPUs), and tell you if it is stable. It will also record the maximum altitude and acceleration, and the time until apogee. All this is very important information if you have built a rocket and want to know what kind of engine you should put in it. Virtual Range estimates the aerodynamic forces acting on the rocket in flight using the US Air Force DATCOM drag methods and Barrowman’s center of pressure method. The simulated flight is displayed with basic, but accurate graphics. This project could not have been completed without the help of Greg Lyzenga and the Rocketry Organization of California. If you have a Macintosh with a G5 or Intel Core CPU, check it out at Ballistic Aerospace Technologies: Virtual Range.

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PerfectFlite MiniAlt/WD on Mac OS X

Matt — Thu, 25 Jun 2009 07:21:58 +0000

My very understanding wife bought me a rocket altimeter. This handy little device will let me control the descent rate of my higher altitude rockets, so they have less time to drift under the parachute. Less drifting means I won’t have to walk a mile across the dry lake bed to retrieve my rocket, and less chance of losing it. Last ROCstock I flew the upgraded Mean Machine on an Aerotech H128W-M. Gary at Rocketography took a nice photo of the launch. It blasted up and out of sight in seconds. I couldn’t find the rocket after a long search, but I got a call a few days later from someone who found it a couple of miles from the launch pad. Anyway, the altimeter is the MiniAlt/WD (MAWD) from PerfectFlite, ordered from What’s Up Hobbies along with the USB adapter. It doesn’t have as many sensors as some other flight computers, and it’s not very programmable, but several people recommended it as a reliable choice for what I want to do. The USB connection is only supported under Windows and Mac OS 9, but I got it to work under OS X. All I had to do was install the drivers from http://www.ftdichip.com/Drivers/VCP.htm, and then do “screen /dev/tty.usbserial-A9009jvE 38400″ from the terminal to talk to it. I even wrote a little C program to download the flight log over the serial port. We’ll see how well it works when I fly the altimeter on Martian Sunrise 2 in a couple of weeks. If that goes well, I’ll look into connecting it to some pyros for dual parachute deployment, probably on the Mean Machine or the new 4″ rocket I’ve been designing.

(Update) Here’s the MAWD dump program with source code: Dump MAWD.dmg. It’s a command line program that takes the path to the serial port as a single argument.

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Your Planet Today Google Gadget

Matt — Sat, 12 Jan 2008 07:14:09 +0000

I’ve finished my first Google Gadget. It’s an up-to date map of the Earth using satellite imagery from the Aqua and Terra observation satellites. The satellite data gets downloaded from NASA GSFC and turned into tiles which work with the Google Maps API. No images older than 36 hours are used. There are other satellite maps available online which are more up to date or more complete, but not both.

Add it to your iGoogle homepage or use the interactive map page.I’ve been working on mapping satellite images off and on for about two years. I have a virtual globe program that downloads the images on the fly and lets you spin and zoom around, but it was never in a state that I could distribute it. The biggest problem was that it makes heavy use of NASA’s web server, and I didn’t think they could take the load if lots of people were using it at the same time. The gadget gets around that problem by hosting a reduced resolution map on my own server. If the load gets too much for my web host, I can make use of Google caching, but that has its own problems. There are some defects in the map stitching. MODIS Rapid Response serves the images as JPEGs, with stuff drawn on them. Also, absent data and heavy cloud cover look exactly the same in the images, so picking them apart is a difficult problem. That’s why there’s some occasional white noise or white regions in the map. Finally, NASA doesn’t publish the geolocated satellite images until about a day after the image is taken, so I had to do it myself using the orbital elements of the satellites. I don’t think the orbital elements are exact enough for this, and I think I have some errors in the algorithm. This means that some parts of the map are shifted slightly from the correct locations.

Still, I think the resulting map came out really good. It’s fun to watch as clouds swirl around, dust blows off the Sahara, snow covers New England, and fires consume my home state.

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